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- Volume 18, Issue 2, 2006
Basin Research - Volume 18, Issue 2, 2006
Volume 18, Issue 2, 2006
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Modelling interactions between fold–thrust belt deformation, foreland flexure and surface mass transport
More LessABSTRACTInteractions between fold and thrust belt deformation, foreland flexure and surface mass transport are investigated using a newly developed mathematical model incorporating fully dynamic coupling between mechanics and surface processes. The mechanical model is two dimensional (plane strain) and includes an elasto‐visco‐plastic rheology. The evolving model is flexurally compensated using an elastic beam formulation. Erosion and deposition at the surface are treated in a simple manner using a linear diffusion equation. The model is solved with the finite element method using a Lagrangian scheme with marker particles. Because the model is particle based, it enables straightforward tracking of stratigraphy and exhumation paths and it can sustain very large strain. It is thus ideally suited to study deformation, erosion and sedimentation in fold–thrust belts and foreland basins.
The model is used to investigate how fold–thrust deformation and foreland basin development is influenced by the non‐dimensional parameter , which can be interpreted as the ratio of the deformation time scale to the time scale for surface processes. Large values of imply that the rate of surface mass transport is significantly greater than the rate of deformation. When , the rates of surface processes are so slow that one observes a classic propagating fold–thrust belt with well‐developed wedge top basins and a largely underfilled foreland flexural depression. Increasing causes (1) deposition to shift progressively from the wedge top into the foredeep, which deepens and may eventually become filled, (2) widespread exhumation of the fold–thrust belt, (3) reduced rates of frontal thrust propagation and possible attainment of a steady‐state orogen width and (4) change in the style and dynamics of deformation. Together, these effects indicate that erosion and sedimentation, rather than passively responding to tectonics, play an active and dynamic role in the development of fold–thrust belts and foreland basins. Results demonstrate that regional differences in the relative rates of surface processes (e.g. because of different climatic settings) may lead to fold–thrust belts and foreland basins with markedly different characteristics. Results also imply that variations in the efficiency of surface processes through time (e.g., because of climate change or the emergence of orogens above sea level) may cause major temporal changes in orogen and basin dynamics.
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Evolution of the late Cenozoic Chaco foreland basin, Southern Bolivia
Authors Cornelius Eji Uba, Christoph Heubeck and Carola HulkaABSTRACTEastward Andean orogenic growth since the late Oligocene led to variable crustal loading, flexural subsidence and foreland basin sedimentation in the Chaco basin. To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin. The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift. These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles. The foreland basin consists of five stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between ∼27 and 14 Ma with the regionally unconformable, thin, easterly sourced fluvial Petaca strata. It represents a significant time interval of low sediment accumulation in a forebulge‐backbulge depocentre. (2) The overlying ∼14–7 Ma‐old Yecua Formation, deposited in marine, fluvial and lacustrine settings, represents increased subsidence rates from thrust‐belt loading outpacing sedimentation rates. It marks the onset of active deformation and the underfilled stage of the foreland basin in a distal foredeep. (3) The overlying ∼7–6 Ma‐old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andean‐derived sediment in the medial‐foredeep depocentre on a distal fluvial megafan. Progradation of syntectonic, wedge‐shaped, westerly sourced, thickening‐ and coarsening‐upward clastics of the (4) ∼6–2.1 Ma‐old Guandacay and (5) ∼2.1 Ma‐to‐Recent Emborozú Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge‐top depocentres, respectively.
Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and flexure by the growing Intra‐ and Subandean fold‐and‐thrust belt.
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Active foreland deformation evidenced by shallow folds and faults affecting late Quaternary shelf–slope deposits (Adriatic Sea, Italy)
Authors Domenico Ridente and Fabio TrincardiABSTRACTA succession of depositional sequences, recording middle‐late Pleistocene and Holocene glacial–interglacial cycles, documents the impact of short‐term tectonic deformation on the western Adriatic margin. The western Adriatic margin is part of the Apennine foreland which was intensely, though variably, deformed during the Meso‐Cenozoic evolution of the Adriatic region from a passive margin to a foreland basin. The study area extends offshore Gargano Promontory, an uplifted sector of the Adriatic foreland, and includes three major deformation belts located along or cross‐strike to the margin: (1) the NW‐SE Gallignani‐Pelagosa ridge, (2) the WSW‐ENE Tremiti‐Pianosa high (both located north of Gargano) and (3) the W‐E to NW‐SE Gondola fault deformation belt (in the south Adriatic). Long‐term deformation along these tectonic lineaments is documented on conventional low‐frequency seismic profiles by regional folds and faults affecting Eocene–Miocene units overlain by dominantly draping Plio‐Quaternary deposits. At this scale of observation, only north of Gargano Promontory there is some evidence of Plio‐Quaternary units thinning against structural highs, thus suggesting that tectonic deformation was protracted through this interval. Based on new high‐resolution seismic data, we show that deformation along these pre‐existing tectonic structures continued during the Quaternary, affecting middle‐late Pleistocene and even Holocene units on the shelf and upper slope north and south of Gargano Promontory. These recent deformations consist of gentle folds and high‐angle faults, locally producing topographic relief that affects the stratigraphy and thickness of syn‐tectonic deposits. We interpret the small‐scale, shallow faults and gentle folds affecting middle‐late Pleistocene and Holocene deposits, north and south Gargano Promontory, as the evidence of ongoing foreland deformation along inherited regional fold and fault systems.
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Use of 40Ar/39Ar K‐feldspar thermochronology in basin thermal history reconstruction: an example from the Big Lake Suite granites, Warburton Basin, South Australia
Authors Sandra McLaren and W. James DunlapABSTRACTThe potential use of 40Ar/39Ar thermochronologic data from K‐feldspars in reconstructing basin thermal history has been evaluated using the example of the Warburton/Cooper/Eromanga Basin, Australia's largest onshore oil‐ and gas‐producing basin. Results from 40Ar/39Ar step‐heating experiments reveal details of the evolution of the basin system, including the following: (1) the operation of high geothermal gradient regimes during the earliest basin evolution, suggesting that basin formation was active rather than passive; (2) slow cooling from a Permo‐Triassic temperature peak of at least 250–300°C; (3) a rise in thermal gradients to contemporary bottom hole temperatures in the last 5–10 Myr; and (4) spatially variable recrystallization events between 100 and 50 Ma and at around 20 Ma. Initial microstructural observations serve as a useful predictor of the quality and nature of the obtainable age information. Data from ‘pristine’ K‐feldspars may constrain the peak temperature conditions experienced in the basin, the basin's early thermal history and also any recent changes in thermal gradient. Contrasting data from texturally modified K‐feldspars may constrain times of thermal transients and/or fluid flow, with the preferred interpretation that K‐feldspars recrystallize in response to such events. The Warburton/Cooper/Eromanga Basin example suggests that the 40Ar/39Ar technique may serve as a useful adjunct to apatite and zircon fission track analysis and conventional organic maturation indices in basin thermal history analysis.
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Parasequence development in the Ediacaran Shuram Formation (Nafun Group, Oman): high‐resolution stratigraphic test for primary origin of negative carbon isotopic ratios
Authors Erwan Le Guerroué, Philip A. Allen and Andrea CozziABSTRACTNeoproterozoic carbonates are known to show exceptional variations in their carbon isotopic ratios, and in the absence of biostratigraphy and a firm geochronological framework, these variations are used as a correlation tool. However, it is controversial whether the carbon isotope record reveals a primary oceanographic signal or secondary effects such as diagenesis. The Shuram Formation of the Nafun Group of Oman allows a stratigraphic test of this problem. The Nafun Group (Huqf Supergroup, Oman) in the Huqf area of east‐central Oman consists of inner carbonate ramp facies of the Khufai Formation overlain by marine, storm‐generated, red and brown siltstones of the Shuram Formation. Towards its top, the Shuram Formation is composed of distinctive shallowing‐upward, 4–17‐m‐thick parasequences cropping out continuously over 35 km, which show recessive swaley cross‐stratified siltstones capped by ledges comprising wave‐rippled, intraclast‐rich ooidal carbonate. These storm‐dominated facies show a regional deepening in palaeobathymetry towards the south. The carbonates of the Shuram Formation are marked by an extreme depletion in 13C in bulk rock. δ13C values quickly reach a nadir of −12‰ just above the Khufai‐Shuram boundary and steadily return to positive values in the overlying mainly dolomitic Buah Formation. The Shuram excursion is thought to be ca. 50 Myr in duration and extends over 600 m of stratigraphy. Carbon isotopic values show a systematic variation in the parasequence stack, with values varying both vertically through the stratigraphy (∼2‰ per 45 m) and laterally in the progradation distance (∼1‰ over 35 km). This supports a primary, oceanographic origin for these extremely negative carbon isotopic values and independently argues strongly against diagenetic resetting.
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Sub‐surface precipitation of salts in supercritical seawater
ABSTRACTExtremely low solubility of typical seawater salts within certain supercritical sections of their pressure–temperature composition space is a proven experimental fact. Its consequences are often referred to as either ‘shock crystallization’ or ‘out‐salting’. Our alternative model for the formation of salt deposits hypothesizes that high temperatures and pressures characteristic for the high heat‐flow zones of tectonically active basins may bring submarine brines into the out‐salting regions and result in the accumulation of geological‐scale salt depositions.
To confirm the laboratory observations, molecular‐scale simulations (molecular dynamics) have been employed to study structural changes in a model seawater system where temperature increased from ambient to near‐critical and supercritical. Fluid properties and phase transition regions extracted from the simulations were then used as input parameters for a reservoir simulator program to model out‐salting in a simple hydrothermal geological system. Both numerical simulations and laboratory experiments confirm that supercritical out‐salting is a viable process of geological significance for the formation and accumulation of evaporites. We suggest two regions where hydrothermally associated salts may be depositing today: Atlantis II Deep, in the Red Sea, and Lake Asale, Ethiopia.
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Volumes & issues
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Volume 36 (2024)
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Volume 35 (2023)
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Volume 34 (2022)
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Volume 33 (2021)
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Volume 32 (2020)
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Volume 31 (2019)
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Volume 30 (2018)
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Volume 29 (2017)
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Volume 28 (2016)
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Volume 27 (2015)
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Volume 26 (2014)
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Volume 25 (2013)
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Volume 24 (2012)
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Volume 23 (2011)
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Volume 22 (2010)
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Volume 21 (2009)
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Volume 20 (2008)
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Volume 19 (2007)
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Volume 18 (2006)
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Volume 17 (2005)
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Volume 16 (2004)
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Volume 15 (2003)
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Volume 14 (2002)
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Volume 13 (2001)
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Volume 12 (2000)
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Volume 11 (1999)
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Volume 10 (1998)
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Volume 9 (1997)
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Volume 8 (1996)
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Volume 7 (1994)
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Volume 6 (1994)
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Volume 5 (1993)
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Volume 4 (1992)
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Volume 3 (1991)
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Volume 2 (1989)
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Volume 1 (1988)